Today's microfluidic chips are capable of reliably carrying out many chemical and reactions and analytical assays using minimal amounts reagents. These high throughput cards incorporate arrays of fluidic networks, each network having a multitude of ports or reservoirs and microchannels associated therewith. Examples of microfluidic chips, fluidic arrays, and their methods use are described in U.S. Pat. Nos. 5,750,015; 6,103,199 and published patent application Ser. No. 99/19717 assigned to the assignee and hereby incorporated by reference. In each network, reservoirs are provided for introduction of sample, reagents, test compounds, or liquid media. In some cases, microfluidic devices are manufactured with media already in the channels or reservoirs as appropriate.
Microfluidic chips have been used for separation and analysis of nucleic acids, proteins and other molecules. By utilizing electrokinetic methods such capillary electrophoresis (CE), dielectrophoresis, and isoelectric focusing, components of a sample can be resolved and analyzed. One method of species detection involves conventional laser induced fluorescence, also known as LIF. A variety of mechanisms known in the art can be used for this purpose. For example, fluorescent detection mechanisms can be used in conjunction with confocal microscopy. Publications such as U.S. Pat. No. 5,296,703 and PCT WO 98/49543 describe systems for detecting fluorescent signals in microchannel arrays.
Desirably, microfluidic chips can be manufactured from a variety of polymer materials leading to user convenience, disposability and affordability. These materials allow for standard manufacturing techniques including injection molding, compression molding, casting or hot embossing. One drawback however is that these methods all require heating and cooling of the chip substrate. Given variations between substrates in glass transition temperatures and varying exposure to both ambient and elevated temperatures, the resulting chips often include some level of warpage and/or minor defects. These irregularities can interfere with the intended operation of the chip. For example, detection systems may include robotics programmed to move to specific locations on a planar card. If the card is warped, these locations are difficult to reach or become inaccessible. Accordingly, it is desired to provide an accurate detection system that can compensate for inherent deficiencies in the microfluidic chip, such as warpage.
Another issue arises due to the fact that the intended application of a microfluidic chip generally dictates its design. For instance, longer CE separation channels are required for sequencing of long nucleic acid sequences while smaller and more concise CE networks can be used to conduct multiplexed enzyme assays. The result is that for different applications, the layout of fluidic network arrays from chip to chip will be different. Conventional analytical systems incorporate circuit (electrode) cards and voltage sources as fixtures. Accordingly, their versatility is limited, usually resulting in expensive systems dedicated to particular applications. For this reason, it is desired to have an analysis and detection system with the versatility to accommodate different chip designs in multiple configurations. Additionally, the chemical and biochemical reactions carried out in microfluidic chips are conducted using small quantities of sample and other fluids that easily evaporate. Therefore, a need also exists for a microfluidic analytical apparatus that alleviates evaporation of fluids within microfluidic chips.